1. Field of the Invention
This invention relates to a battery charge remaining detector for detecting charged and discharged currents of a battery in order to detect a battery charge remaining.
2. Description of the Prior Art
Battery-driven equipment, e.g. a notebook type personal computer, is commonly used, and a rechargeable battery is used as a power source therefor. In such equipment, how long it can be used without recharging can be known when its battery charge remaining is indicated. Therefore, it is known that some equipment can indicate a battery charge remaining.
To indicate a battery charge remaining, it is first necessary to measure the battery charge remaining. For measuring the battery charge remaining, certain methods, such as the measurement of a battery voltage and the integration of charged and discharged quantities, are known. A method for measuring a battery voltage is easy, but a battery such as a nickel-hydrogen battery does not indicate a change in its voltage unless its remaining capacity is lowered substantially. Therefore, its remaining capacity cannot be measured accurately. There is also a problem that a temperature change affects the battery voltage, making it impossible to accurately measure the remaining capacity.
On the other hand, a discharged quantity of a battery can be relatively easily totaled up because the discharged quantity can be measured relatively accurately in view of the charged and discharged currents after full charging, and a circuit for measuring is not so complex. Therefore, this totalization of the discharged quantity is often used for measuring the battery charge remaining.
However, in the above totalization of the charged and discharged quantities, a current flows in opposite directions when being charged and discharged. Consequently, the detection of the charged and discharged currents requires the following measures:
(i) a power source which outputs a negative voltage is provided to enable an input voltage area of an amplification circuit to be expanded in the negative direction, or PA1 (ii) current detecting elements for detecting currents which flow in opposite directions are disposed to enable the detection of the charged and discharged currents by passing a current through either of the current detecting elements according to charged and discharged states by switching a changeover switch. PA1 a current-voltage convertor which is disposed on the negative electrode side of the battery and outputs a value of a current passing through the battery as an output voltage, PA1 a voltage synthesizer which adds a predetermined positive voltage to the output voltage of the current-voltage convertor to output a sample voltage, and PA1 a current signal generator which generates a signal for the charged and discharged currents of the battery on the basis of the above sample voltage.
Thus, the above method has a disadvantage that a circuit for detecting the charged and discharged currents becomes complex.
Battery-driven notebook type personal computers are particularly required to have a lower number of parts because they are produced to be small, lightweight and inexpensive.
On the other hand, the continuously usable time of such equipment has been extended thanks to power-saving circuits and high-performance batteries. Accordingly, it has become necessary for a battery charge remaining to be detected very accurately. Specifically, when the continuous use was limited to about one to two hours after full charging, an error in detecting a battery charge remaining did not have a significant impact. However, when the continuous use can be extended up to seven or eight hours, an error of one to two hours has a large effect.